Conventionally, there is known a vehicle environment monitoring device that includes: an imaging device that captures an image of a monitoring region; a light projector that radiates pattern light (a bright spot pattern) in the monitoring region; a data processing unit that detects existence of an obstacle or the like by processing image data of reflected light of the pattern light generated by an imaging device; and a switching means that displays the obstacle or the like detected by a data processing unit on a display device, instead of a state of the monitoring region, when an illumination intensity around a vehicle is equal to or lower than a predetermined value (for example, refer to patent reference 1).
Moreover, a method that enables optical distance measurement is proposed. For example, this method includes: a step of projecting a primary speckle pattern from a lighting assembly into a target region; a step of capturing a plurality of reference images of the primary speckle pattern; a step of capturing a test image of the primary speckle pattern projected on a surface of an object in the target region; a step of comparing the test image with the reference images in order to identify the reference image that includes the primary speckle pattern that matches most closely the primary speckle pattern in the test image; and a step of estimating the position of the object on the basis of the distance of the identified reference image from the lighting assembly (for example, refer to patent reference 2).
However, in the above conventional device and method, it is necessary to perform computation for calculating a correlation value by pattern matching between a captured image and a plurality of reference images, and there is a problem that the computation amount of this computation is large.
Hence, there is proposed a method in which a quadrangle pattern with four linked light dots, that is, a light spot appears periodically in projected pattern light, and the light spot is distinguished from other light spots by a combination of illumination and non-illumination of light dots around the light spot (for example, refer to patent reference 3).